Inflate handle view as part of expanded view layout

We need an id for the handle view so that we can reference it in the
integration.
Move inflation of the handle view from the expanded view class to the
layout. This allows us to specify a resource id for it.

Bug: 283991264
Test: open a bubble from bubble bar
Test: atest PlatformScenarioTests:android.platform.test.scenario.sysui.bubble.BubbleBarTest
Change-Id: I55319b989bf953c8c4f856242d1ca4abdf8ede1b